1. Field of the Invention
The present invention relates to an image reading apparatus for reading fingerprint image data.
2. Description of the Related Art
Recently, a fingerprint recognition apparatus (fingerprint image reading apparatus) has been used. This apparatus reads a fingerprint of a person and recognizes it to identify the person.
A fingerprint recognition apparatus using a two-dimensional plane sensor or a one-dimensional line sensor (one-dimensional image pickup device) is proposed. The apparatus using a one-dimensional line sensor has a transparent, flat plate in a fingerprint reading position. A light source for illumination, a rod lens group (a SELFOC lens) and a line sensor are arranged under the transparent, flat plate.
Another fingerprint recognition apparatus using a line sensor is proposed in which the line sensor is incorporated into a hollow, transparent roller. In this apparatus, a user moves his or her finger and presses it on the transparent roller. The line sensor reads a fingerprint image of the pressed finger. A given printing pattern is printed on the outer surface of an end portion of the transparent roller. The line sensor reads the printing pattern as well as the fingerprint image and senses variations in the printing pattern to determine image data reading timing.
In general, an apparatus using a line sensor has to read reference white and black images and prepare adjustment data in advance in order to correct the influence of differences in characteristics between image pickup elements and lens optical systems which configure the line sensor.
To determine a read image by a predetermined reference value is likely to make the operation more unstable because the apparatus using an optical image pickup element is affected by variations in outside light or variations in light source due to a decrease in battery voltage, even though it prepares correction data.